1. Field of the Invention
The present invention relates to an ink jet ink, an ink jet recording method, an ink cartridge, a recording unit and an ink jet recording apparatus.
2. Description of the Related Art
An ink jet recording method is a method of forming images by applying ink droplets to recording media such as plain paper and glossy media. This method has rapidly come into widespread use by the reduction in cost and improvement in recording speed of ink jet recording apparatuses. Further, with the rapid spread of digital cameras in addition to the progress in obtaining high-quality images by the ink jet recording method, the ink jet recording method has been commonly used as the output method of images equal to silver halide photographs.
In recent years, further progress in obtaining high-quality images is achieved by minimization of ink droplets and improvement in the color gamut accompanying introduction of a multicolor ink. On the other hand, the demand to a coloring material and ink becomes higher, wherein severer properties are demanded in the improvement in color developabilities and reliability of clogging and ejection stability.
On the other hand, it is mentioned that the ink jet recording method is inferior in the image storage stability of the obtained recorded matter, as a problem of the ink jet recording method. Generally, the image storage stability of the recorded matter obtained by the ink jet recording method is low as compared with silver halide photographs. When a recorded matter is specifically exposed to light, humidity, heat, the environmental gas that is present in the air, etc. for a long time, there is a problem that the coloring material on the recorded matter deteriorates and is easy to generate the change of color tone and fading of images.
Among image storage stabilities, an especially large number of proposals have been made to improve the lightfastness of an image. Among cyan, magenta and yellow inks, yellow ink has especially low lightfastness of an image. A coloring material has been proposed which can, for example, improve lightfastness of an image, and form images having excellent color developabilities (see WO 2006/082669).
On the other hand, there have been proposals concerning inks which contain a material (buffer agent etc.) having a pH buffering effect in order to suppress the effects of a change in pH of the ink (deposition of the coloring material, corrosion of parts in contact with the ink etc.) (See Japanese Patent Application Laid-Open Nos. H01-149872, H06-166840 and H06-220386).
Among yellow, magenta and cyan inks, which are widely used for ink jet ink, yellow ink tends to have especially poor lightfastness of an image. Therefore, the present inventors thought that there was a need for detailed investigation into the coloring materials used in yellow ink.